Fundamental investigations on the influence of high effective ion temperatures on the kinetics of ion-molecule reactions in the gas phase using high kinetic energy ion mobility spectrometry with selective ion sources

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The objectives of this continuation project are a) a detailed description of the kinetics of ion-molecule reactions in the gas phase as a function of the effective ion temperature on the basis of experimental investigations and b) the development of the required instrumentation in the form of a high kinetic energy ion mobility spectrometer (HiKE-IMS) with selective ion sources. While extensive data are available for room temperature to describe the kinetics of various gas phase reactions, only very few data are available for higher temperatures. Especially, experimental investigations on the kinetics of cluster association and dissociation reactions are hardly available. It is generally known that an increase in ion temperature influences the internal energy states and interaction energies between ions and neutral gas molecules and thus dissociation and fragmentation processes and the conversion rates of gas phase reactions. Within the scope of this continuation, these effects occurring at elevated ion temperatures will be fundamentally investigated. Kinetic and dynamic simulations of the processes, together with the experimental data, will finally provide new insights into the temperature-dependent kinetics of gas phase reactions, which are not only of academic interest, but also allow an application-specific optimization of the HiKE-IMS for sensitive and selective detection of certain target compounds. However, such experimental investigations require that no other reactive ions apart from the target reaction system are present in the HiKE-IMS, since parallel reactions make a clear interpretation of the measurement results difficult or impossible. The HiKE-IMS from the previous project does not yet fulfil this requirement, which is mainly due to the corona discharge source used. Within the scope of the continuation, a hollow cathode ion source compatible with the HiKE-IMS will be realized instead in order to generate defined ion populations. In addition, a laser ionization source is planned for ionizing molecules via resonant multiphoton excitation. In particular, medium polar to non-polar aromatic substances can be ionized very selectively, and tunable lasers can be used to investigate other substance classes. In addition, ions can be generated in a spatially and temporally very defined range in order to vary the residence time of the ions in the reaction region by varying the ionization site independently of other parameters. This time variation enables the calculation of reaction rates and reaction rate constants. For this purpose, a HiKE-IMS will be realized with locally variable coupling of the laser beam into the reaction region.